JEE Main2014PhysicsUnits and DimensionsActual
From the following combinations of physical constants (expressed through their usual symbols) the only combination, that would have the same value in different systems of units, is:
Options
- Ach 2 _ o ^2
- Be ^2 2 _ o Gm _ e ^2
- C_ o _ o c ^2 G he ^2
- D2 _ o _ o ce ^2 h G
Correct answer
B. e ^2 2 _ o Gm _ e ^2
Step-by-step solution
The dimensional formulae of aligned & e = [ M ^0 ~L ^0 ~T ^1 ~A ^1 ] & ₀= [ M ⁻¹ ~L ^3 ~T ^4 ~A ^2 ] & G = [ M ⁻¹ ~L ^3 ~T ⁻² ] & and m _ e = [ M ^1 ~L ^0 ~T ^0 ] & Now, e ^2 2 ₀ Gm _ e ^2 &= [ M ^0 ~L ^0 ~T ^1 ~A ^1 ]^2 2 [ M ⁻¹ ~L ⁻³ ~T ^4 ~A ^2 ] [ M ⁻¹ ~L ^3 ~T ⁻² ] [ M ^1 ~L ^0 ~T ^0 ]^2 aligned aligned &= [ T ^2 ~A ^2 ] 2 [ M ⁻¹⁻¹⁺² ~L ⁻³⁺³ ~T ⁴⁻² ~A ^2 ] &= [ T ^2 ~A ^2 ] 2 [ M ^0 ~L ^0 ~T ^2 ~A ^2 ] = 1 2 aligned 1 2 is dimensionless thus the combination e ^2 2 ₀ Gm _ e ^2 would have the same value in diffe